The water cycle
Long before the biblical David slew Goliath with a stone, our ancestors are said to have walked across continents with their blunt stone implements and flint stones, burning and killing 'mega fauna'. However, we don't need such old fashioned tools anymore, we just have to use Thomas Crapper's useful invention to kill what remains.
I found this wall in a studio that's housed in a scrapyard, which like all other scrapyards is situated on the banks of a Nullah. This one, the drain that starts from Lalbagh and flows east.